Assessment Of Ischemic Penumbra Using Aquaporins Magnetic Resonance Molecular Imaging

Objective: The aim of the study was to investigate the diagnostic value of ischemic penumbra using multiple b-value diffusion weighted aquaporin magnetic resonance molecular imaging(AQP-MRI).We also further investigate the relevances between MR imagings and histopathology of ischemic stroke and the expression of AQP4.Methods: A total of 70 Sprague-Dawley rats were divided randomly into two groups: 58 rats for stroke group and 12 rats for control group.The stroke group established transient cerebral ischemic models by middle cerebral artery occlusion(MCAo)for one hour.The first part consisted of 30 rats for neurologic deficit scores and multimodality magnetic resonance imaging,including 25 rats of stroke group(divided into 5 subgroups on average,1h?3h?6h?24h?48h after stroke)and 5 rats of control group.After MR scanning,all of the rats were sacrificed for western blot detection.The second part consisted of 40 rats,33 rats for stroke group and 7 rats for control group,which were randomly divided into 3 groups:(1)Hematoxylin-eosin stain: 15 rats of stroke group(divided into 5 subgroups on average,1h?3h?6h?24h?48h after stroke)and 3 rats of control group;(2)Transmission electron microscopy detection: 3 rats of stroke group(24h after stroke)and 1 rat of control group;(3)Immunofluorescence staining: 15 rats of stroke group(divided into 5 subgroups on average,1h?3h?6h?24h?48h after stroke)and 3 rats of control group.MR acquisition sequences contained T2-FLAIR?DWI?ASL and AQP-MRI(18b value DWI).Then relative areas and ratios of the lesions were measured for all of the imagings.The areas of AQP-MRI/T2-FLAIR mismatch were compared with that of DWI/T2-FLAIR mismatch and ASL/DWI mismatch to verified the diagnostic value of AQP-MRI for the ischemic penumbra.The evaluation was performed in combination with histopathology.The information of the imagings were associated with histopathology and AQP4 expression by hematoxylin-eosin stain,transmission electron microscopy,western blot and immunofluorescence.Results: The concrol group rats had no neurological dysfunction.While the stroke group rats presented with various degrees of neurological dysfunction,and got worse over time.There was no special finding in MR imagings of the control group.While in the stroke group,we could find wide range penumbra areas within 6 hours according to AQP-MRI/T2-FLAIR mismatch,then the penumbra areas shrinked rapidly from 6h to 24 h,and almost disappeared in 24 h.The result showed that there was significant difference between the areas of AQP/T2-FLAIR mismatch and that of DWI/T2-FLAIR mismatch within 24 hours(P<0.01).However,there was no significant difference between the areas of AQP/T2-FLAIR mismatch and that of ASL/DWI mismatch within 6 hours(P>0.05).ASL-CBF showed hypertransfusion in 24 hours after stroke.The relative ratios between penumbra areas(r IP)and the core(r IC),peripheral normal brain tissues(r NC)had significant differences respectively(P=0.001 and P<0.05).Histopathology findings revealed that the morphology and structure of neurons in the penumbra areas were different from that in core and normal brain tissues.MR imagings were corresponded to histopathology.In 24 hour time point,r AQP-ADC value of basal ganglia and cortex of lesion side showed in AQP-MRI had significant difference(P<0.01).AQP-MR imaging could visualized the differences.The AQP-ADC values of peripheral to the penumbra in the ipsilateral area were much higher than that in the contralateral(P<0.05).The expression of AQP4 was increased after ischemic stroke,and presented double peak in 1hour and 6 hour time points.Conclusion: Compared with traditional mismatch,AQP-MRI/T2-FLAIR mismatch might visualized ischemic penumbra with multi-layer and more accurate.MR imagings were corresponded to histopathology.AQP-MRI combined with T2-FLAIR could provide valuable information for the assessment of ischemic penumbra.AQP-MRI was a visual imaging,could provide important micro informations for ischemic stroke.The expression of AQP4 was increased after ischemic stroke,and presented dynamic changes.It was not a simple linear correlation between MRI findings and AQP4 expression.